1. Field of the Invention
The present invention generally relates to a cooling device using a liquid, such as water, as coolant, for cooling particularly a computer system, and in particular to a pump of the cooling device that circulates the liquid coolant through the cooling device wherein the pump comprises a permanent magnet rotor comprising upper and lower sections having magnetic poles arranged in a non-symmetric alternating manner in order to ensure smooth starting of the pump and to enhance performance of the cooling device.
2. The Related Art
A conventional water pump comprises a single permanent magnet to interact with an electrical magnet that is formed of silicon steel plates inducing a time-variable magnetic field to drive a blade assembly for drawing and expelling water. The permanent magnet is arranged to have north and south poles thereof opposing the magnetic poles of the electric magnet so that the repulsive force between magnetic poles of the magnets rotates the permanent magnet about a constant axis. However, when the permanent magnet is not in rotation, at least one of the magnetic poles of the permanent magnet becomes attractive with an opposite pole of the electric magnet whereby when the pump is started again, such an attraction forces becomes a resistance against the initial rotation of the rotor, and causes vibration or shake when the rotor eventually gets moved. This often results in un-smooth starting of the pump and deteriorates the performance of the cooling system.
Such a problem may get even severer when the cooling device is used to control temperature of high-speed electronic devices, such as a central processing unit of a computer. Due to the fast development of the computer industry, the central processing unit or other electronic devices must process data and instructions in an extreme high speed, which means a great amount of heat is generated in a very short period. Such a fast accumulation of excessive heat must be properly removed. When a conventional cooling device, such as that just described, is employed to cool the electronic devices, the poor performance of the cooling device, even occurring only in a short period at the starting thereof, may probably cause heat damage to the electronic devices due to not timely removing the excessive heat.
Thus, it is desired to provide a liquid based cooling device that eliminates the drawback of non-smooth starting of pump often observed in the conventional designs.